At 18 months it'd be congenital most likely imo. Do you know anything about his background at all?

When is the vet appointment?

My gut hunch is to risk a small amount. Fwiw.

EDIT: yes, Lasix first. *Small* amount, again, a portion of normal dosing, but Lasix has a range of dosing. I just don't want to dehydrate him and throw off his electrolyte balance with an arrhythmia already present.

Hi Guys, Del Boy is currently residing with me. BamBam and I have been unable to get any appointment with an "exotics" vet until Tuesday, but he had been holding his own now the weather is cooler.
However, this evening he appears to be struggling more, although he remains alert and relatively active, possibly more active than usual. He is eating and drinking normally.
His arrhythmia continues although his lungs sound clear. His ear margins are dark, as are his lips. I have got an appointment with a cat and dog vet tomorrow morning as an emergency, but will see the out of hours vet if he deteriorates further.
He is a foster from the RSPCA. With that in mind, is there anything I can be doing in the way of supportive management?

Thanks Lynx. We haven't been able to try Lasix yet. As he's a foster from the RSPCA we are limited as to what we can do without vet approval. I do have a vet appointment later today so hope I may be able to persuade the vet to try Lasix and Vetmedin. I'm now more convinced than ever that he has a heart problem as I heard him hooting whilst he was eating his vegs just now.
Will let you know what the vet says.

Del Boy was seen by the vet this lunchtime. She was very thorough and seemed quite knowledgeable, despite not being an expert in guinea pigs. She couldn't find anything to suggest this was heart related (despite me taking the heart info with me, which she was quite receptive to). However, she was extremely concerned about his lungs and was more convinced this is a lung related problem, especially as there was a lot of inspiratory noise, where she would have expected more expiratory noise. We discussed the pros and cons of an Xray and the necessary GA, as he is an extremely skittish pig, and decided to go ahead.

Fortunately, they were able to Xray him without the need for sedation or GA and surprisingly, the Xray has shown almost complete white out of both lungs, suggestive of pneumonia. His heart outline was normal. They gave him oxygen but that did not improve his colour much, so they think the dark lips and ears are his normal colouring. (I remain to be convinced). He has been started on Baytril and sent home, since there is nothing they can do that I can't do here.

He's not out of the woods by any means and I will be watching both him and his brother like a hawk. I'll keep you all posted.

I'm really glad to hear that the vet was knowledgeable, thorough and open to heart issues despite not being an exotics expert. The difference between inspiratory and expiratory sounds I've run into before, from a vet with asthma herself. This vet sounds good.

Thanks Talishan and Lynx. Del Boy is holding his own. At least he's still with us!

Yes, his breathing continues to be laboured. He is using his abdominal muscles and his nostrils are flaring with each breath. He is still eating (despite Baytril) and is still bullying his brother Rodney, which I take to be a good sign. At least it's his normal behaviour.

He's had one dose of intra-muscular Baytril and two oral doses but doesn't seem to have improved at all. I assume I'm being impatient. I assume it will take a couple of days before we see any sign of improvement? Would it be worth giving him some metacam as well? Having recently had pneumonia myself, I know how rough it made me feel.